The UK energy system has in the past been characterised by the ownership and control of large-scale supply technologies by corporate entities. It has become apparent however that such structures are ill suited to addressing contemporary energy challenges of decarbonisation, energy security and affordability. Moreover, their resistance to change means that the current system is fundamentally inconsistent with the need for energy system change. The advent of affordable renewable energy however, particularly at small-scale, offers new prospects for addressing these energy challenges. In particular, they present an opportunity for greater societal engagement in the energy system, not least as owners and managers of energy assets, but also as stakeholders with interest and influence in the energy system more generally. Within the context of greater citizen engagement in energy, community energy has developed in the UK as an organised means for “collective action to purchase, manage and generate energy” (DECC, 2014b). Such collective action is complimented by progressively broad engagement by individuals in the energy system as investors and prosumers, rather than solely consumers. This thesis responds to a need to better understand the role and value of community energy, and wider societal engagement more generally, within the wider energy system. Taking a mixed-methods approach, this thesis contends that community energy has the potential to have significant impacts at both local and national scales. Social, economic and environmental impacts of a specific community energy project are evidenced to illustrate the breadth and scale of potential impacts at the local level. Broader analysis of the community energy movement, and of ‘small-scale energy’ more generally is suggestive of the potential for such approaches to be transformative in terms of overcoming system inertia. In particular, the energy system is undergoing a process of democratisation, whereby power, wealth and value is gradually distributed among society. A key role for policymakers then is to consider the strategic importance of democratisation.